从子类调用超类方法

Question

我正在为一个银行帐户建模，其中包含一个不能透支的超类 Account 和一个子类 SavingsAccount。 makeWithdrawal()方法，在主类调用时，应检查提款是否大于余额并提示输入，然后编辑余额。

如何从Account 调用makeWithdrawal() 方法并在SavingsAccount 中使用super 关键字覆盖它？我的编译器给了我“错误：不兼容的类型：缺少返回值。

Account中的方法：

double makeWithdrawal(double withdrawal)    {
    return balance -= withdrawal;
}

（很简单。）这个方法最初是抽象的，但它会导致错误。

SavingsAccount中的方法：

    public double makeWithdrawal(double withdrawal) {
        double tempbalance = getBalance();
        if (withdrawal > getBalance())  {
            withdrawal = Input.getDouble("Your withdrawal cannot be larger than your balance. Enter a withdrawal <= "+getBalance());
            return;
        }
        else    {
            return super.makeWithdrawal(withdrawal);
            }
    }

Answer 1

问题不在于您致电super.makeWithdrawl()，这是正确的。它在它上面的if 子句中带有空的return 语句。您获取更新提款金额的逻辑是明智的，但是您需要在执行此操作时返回新余额。我建议将呼叫转移到条件之外的super.makeWithdrawl()：

if(withdrawal > getBalance())  {
    withdrawal = Input.getDouble("Your withdrawal cannot be larger than your balance. Enter a withdrawal <= "+getBalance());
}
return super.makeWithdrawal(withdrawal);

如果原始提款金额太大，这将使用更新后的提款金额。

Answer 2

问题出在

返回；

你应该用

替换它

退货；

    public double makeWithdrawal(double withdrawal) {
    double tempbalance = getBalance();
    if (withdrawal > getBalance())  {
        withdrawal = Input.getDouble("Your withdrawal cannot be larger than your balance. Enter a withdrawal <= "+getBalance());
        return withdrawal;
    }
    else    {
        return super.makeWithdrawal(withdrawal);
        }
}

Answer 3

如果

if (withdrawal > getBalance())  {
            withdrawal = Input.getDouble("Your withdrawal cannot be larger than your balance. Enter a withdrawal <= "+getBalance());
            return;
        }

你需要返回双精度值而不是简单的返回。

Answer 4

如果我理解正确的话：

Account 是基类，SavingsAccount 是子类？

然后：super.makeWithdrawal(withdrawal);

还要确保在定义类时继承：

public class SavingsAccount extends Account{...}